The invention relates to a device for connecting a generator (or alternator) to a belt drive of an internal combustion engine, comprising a belt pulley that is guided so that it can rotate relative to a hub set on a shaft, wherein at least one spring element arranged between the belt pulley and hub connects the belt pulley and the hub to each other elastically for transferring rotational motion and in this way sets a relative rotation between the belt pulley and hub according to an effective torsional stiffness.
For powering the on-board power network of a motor vehicle, a generator is typically provided in the area of the internal combustion engine, wherein this generator is connected via a belt drive to a crankshaft of the internal combustion engine and is set in rotation by the engine when the internal combustion engine is running. This rotation generates the current required for operating the electrical load and for charging the starter battery.
The characteristic rotational irregularities of the internal combustion engine, however, lead to the introduction of forces and resonances into the belt drive, which would lead, in the case of a rigid connection to the secondary assemblies, to strong oscillations in its drive. In order to reduce this effect, devices are typically provided between the belt drive and the corresponding assembly, in order to achieve decoupling from the crankshaft of the internal combustion engine.
From DE 10 2006 057 793 A1, a device of this type is known for connecting a secondary assembly, such as, for example, a generator, to a crankshaft by means of a belt drive. This device comprises a belt pulley that is guided so that it can rotate by a bearing relative to a hub that is placed on a shaft of the secondary assembly. In order to allow a transfer of the rotational motion of the belt drive from the belt pulley to the hub and to simultaneously equalize the rotational irregularities of the internal combustion engine introduced into the belt drive, between the belt pulley and the hub there are three spring elements that connect the belt pulley and the hub to each other elastically and that allow a relative rotation between both elements according to an effective torsional stiffness.
A disadvantage in a device of the state of the art is that, through the arrangement of the spring elements between the belt pulley and hub, only one, constant torsional stiffness is defined. However, in the case of belt-driven generators, it is desirable to use a device with the smallest possible torsional stiffness in the case of a small load on the generator, in order to decouple the generator to a large extent from the belt drive. In the case of a large load on the generator due to a higher current draw, a small torsional stiffness generates a very wide relative rotation between the belt pulley and the hub due to the counter moment generated by the current draw in the generator. In order to prevent this, in turn, and in order to keep the operating range of the device small, a high torsional stiffness is consequently desired for a high load on the generator. Typically, therefore, in the case of a device of the state of the art for connecting a generator to the belt drive of an internal combustion engine, a compromise solution is reached between a small torsional stiffness and a higher torsional stiffness.